the datahseet says .33uF cap on INPUT.. and a 0.1uF on OUTPUT..
My question is...
1.) When you see things like in the datasheet.. how do you know what TYPE of cap to use.
My guess is that the symbol will be marked with polarity if it needs to be a electrolytic type cap... yes?
If they do NOT have any polarity markings... then you should use....? A ceramic type of cap?
What would be the negative effects of using 2 x electrolytic caps on the input/output sides of the 7805 regulator? (anything?)
I read that most linear regulator datasheets suggest tantalum or electrolytic capacitors as they have higher ESR... so elec type SHOULD always be used? (for this 7805 regulator type)
I was going to be supplying some links to caps to order to a friend... and started to have these questions.. when trying to find .33uF caps for sale..
I have some 33uF elec caps on hand.. but no .33uF ones? (hence the search for a link to order from.. and the questions/post)
As I understand it.. these caps are more for noise filtering?
Is there any 'range' I am safe with? Or are the specific values crucial? (I wouldnt think so unless lower values were used?)
Electrolytic capacitors (including tantalum) are polarized. Other capacitor types are not.
Electrolytic capacitors don't "act like" capacitors at high frequencies. In fact, they can become inductive with their impedance increasing at high frequencies.
If a voltage regulator (or other IC) becomes unstable and oscillates, it's usually going to oscillate at a very-high frequency (somewhere in the MHZ range).
So, we need a non-electrolytic capacitor to create a low-impedance "short" for any high-frequencies. You can have an electrolytic in parallel for better filtering at lower frequencies.
Stability/instability is related to the negative feedback which holds the voltage constant under varying conditions. If there's enough phase-shift for that feedback to become positive you get an oscillator. It get's mathematically very complicated and I don't understand it... I think it has something do with [u]Laplace Transforms[/u]. I took a class about it a million years ago, but I never applied it to the real world and I don't remember. But even if you know the math, we don't know enough about the internal physics of the 7805 to make the calculations. And, there's a good chance that whoever developed the 7805 chip doesn't know either... They probably determined that a capacitor was required experimentally...
Value of the capacitor is not critical, for 500mA load it is enough 470uF and 0.1uF on both sides. If you are dealing with low signal (1mV) then you consider the noise. By theory tantalum capacitor shouldbe the best in ptactice they ar not.
To find out you have a good or not capacitor is look at Vcc on osciloskope. Not long time ago I had a problem with noisy capacitors, I was trying about 20 of them and find only one electrolic working ok ( I have 10 of them fron one supplyier and every one of it is ok )
And the noice was not generated by power supply but in op amp woltage divider.
SoI threw away op amp and replaced it by single transistor - noise 100 lower.
The first drawing - add 0.1uF on both sides -theory,in practice - very often no difference.
On the left - capacitor can be 16V, on right 6.3V.
Value of the capacitors is related to load current, for 100 mA 10uF it is ok, for 1000mA - 1000uF - never to much.
The ESR of a capacitor can be important for stability - too high or too low can be a problem, sometimes
the poor ESR of an electrolytic is what is needed to avoid high frequency oscillation.
Every voltage regulator is different, and some datasheets don't give much information.
The old 78XX and 79XX linear regulators are pretty relaxed in their requirements for capacitors,
as they are emitter-follower output stages. LDO regulators can be much more fussy, and in
particular their tendancy to oscillate depends strongly on voltage headroom and load current.
Read what datasheet you can find, be prepared to experiment if unsure (but with a dummy load
that won't get fried if oscillation breaks out).
I have bread boarded everything up and tested for weeks.... but when it came to using the actual correct cap values/types I wanted to get some feedback on some things.
1.) So many different 7805 diagrams..
2.) datasheet didnt show polarized caps.. so I wanted to ask if using electrolytic types would be a problem instead of ceramic disc types
No scope... (wouldnt now how to use it if I did unfortunately)
picture/block diagram will help.
I don't think your problem is in capacitors, probably you need seperate 5V for your neopixel rings, can you measure how much current they are taking when connected to 5 V ?
I just want to be correct in the values and types of caps I use in the END.
I have no problems outside of that.
My project has had zero faults in behavior.. but when I take these to a final PCB.. I wanted to be clear about the caps values (as so many diagrams show different values)..
then I wanted to clarify to myself about using polarized caps vs ceramic caps..
On my current breadboard set-up.. I have been using 4.7uF elec cap on the INPUT.. and a 01.uF ceramic cap on the output.
That doesnt exactly follow the diagams posted around.. nor the datasheet.
If your toys are working ok with those capacitors then use them.
As I mentioned before the value of capacitors are not critical .
Electrolytic capacitors are for filtering low frequency (audio), ceramic for high frequences (RF)
